Smart glass may mean it is curtains for window blinds

A 'smart' window that can block out sunlight or heat at the flick of a switch
may make blinds and curtains redundant.

A dual-band electrochromic material has been developed by linking tin-doped indium oxide nanocrystals to an amorphous niobium oxide matrix. These transparent films are capable of blocking solar radiation in a controlled fashion, allowing daylight and solar heat to be selectively and dynamically modulated through windows.Photo: ANNA LLORDES/LAWRENCE BERKELEY NATIONAL LAB

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Dr Anna Llordes, who led the research at the Lawrence Berkeley National Laboratory in California, said: "The resulting material demonstrates a previously unrealised optical switching behaviour that will enable the dynamic control of solar radiation transmittance through windows.

"These transparent films can block near-infrared and visible light selectively and independently by varying the applied electrochemical voltage over a range of 2.5 volts."

The reason why the glass has the ability to block out both heat, in the form of infrared radiation, and visible light is because the indium tin oxide nanocrystals and the niobium oxide glass both respond differently when an electric current is applied across them.

They are what is known as electrochromic. When a small negative charge is applied to the glass, it causes the indium tin oxide nanocrystals to absorb infrared light.

If that charge is made more negative then the niobium oxide absorbs visible light.

This means that a window can be tuned to simply dim or to block out light altogether.

The researchers also found that combining the two materials into a single glass caused the niobium oxide to block out five times as much light as it would by itself.

Dr Delia Milliron, the principal investigator on the project, said they hoped to improve the amount of infrared light that can be blocked.

She believes the cost could be brought down to produce glass that is just 10 to 15 per cent more expensive than a standard window.

"Integrating our active glass with a solid electrolyte and a transparent counter electrode, suitable for a real window prototype, is the subject of our current research," she said.